Epoxy resin compositions cured with reaction products of dicarboxylic anhydrides, aliphatic diols and tertiary amines



United States Patent ice EPQXY RESEN CGIt EPQSHIGNS CURED WITH RE-ACTEON PRODUQTS 01 DKIARBQXYLIC ANH"- DRlDES, ALIPHATIC BIGLS ANDTERTEARY AMINES Leo S. Kuhn, Schenectady, N.Y., and John If. Keane,

Pittsfieid, Mass., assignors to General Electric Company, a corporationof New York No Drawing. Filed Dec. 20, 1962, Ser. No. 246,009

'7 Claims. (Cl. 260-47) This invention relates to new and useful epoxyresin compositions. More particularly, the invention relates to suchcompositions which are possessed of desirable physical, chemical andelectrical properties, including a desirably long pot life and which areparticularly characterized by their elastomeric quality both at roomtemperature and elevated temperatures, which makes them particularlyuseful for coating, impregnating and potting structures which must beelectrically insulated without failure while subjected to mechanicalstress at high temperatures.

Epoxy, epoxide or ethoxyline resins, as they are variously called, arewell known in the art. Generally, such epoxy resins contain an averageof more than one epoxy group per molecule and comprise polyetherderivatives of polyhydric organic compounds, such derivatives containing1,2 epoxy groups, the compound being selected from the class consistingof polyhydric alcohols and phenols containing at least two phenolicgroups. A typical epoxy resin is disclosed in Us. Patent 2,324,483 toCastan wherein there is described the reaction product of phenols havingat least two phenolic hydroxy groups and an epihalohydrin, such asepichlorohydrin, such reaction product having at least two epoxy groupsand curing to a thermoset, infusible mass by the use of a carboxylic orpolybasic acid or acid anhydride. In U.S. Patent 2,444,333, there isdescribed the use of organic nitrogen base or amine type materials forcuring epoxy resins, such materials often giving a rapid cure at roomtemperature.

Generally speaking, the hard and rather brittle epoxy resin compositionsnormally attained with polybasic acid or anhydride or amine type curesare useful in many applications. However, in some cases it is requiredthat such resins be used as adhesives, coatings or bonding compounds inconjunction with other structures such as electrical conductors,laminates, and the like, which expand or move either at room temperatureor at elevated temperatures under the stresses of the machines in whichthey may be used. In such cases it is required that the resincompositions used be rubbery or flexible to prevent the disruptiveforces from tearing the structure apart with resultant failure. Thus,when the ends of stator coils of electrodynamic machines are dipped inand sealed with a resinous material, it is desirable that at highoperating temperatures of the order of 100 C.l25 C. and above, theinsulating resin be rubbery and flexible so that it will conform to theexpansion and warping of the stator coil end turns without breaking theseal and without destroying the insulation. By this is not meant simplyheat distortion of the material which is permanent, but an ability toyield under high temperature produced stresses and to recover therefromupon release of the stress.

A principal object of the invention is to provide new epoxy resincompositions which have desirable physical, chemical and electricalcharacteristics and which are characterized by an elastomeric quality,particularly at elevated temperatures which makes them useful forcoating, impregnating and dipping electrical apparatus and otherstructures.

Patented Mar. 28, 1967 Briefly, the invention comprises epoxy resincompositions of very limited composition and characteristics which arecured with particular reaction products of anhydrides and diols atrestricted temperatures, such cure being accelerated and directed by theuse of tertiary amines to produce long chain elastomeric products ratherthan highly cross-linked rigid materials.

The ethoxyline resins used in conjunction with the invention are, aspointed out, well known in the art. It has been found that the onlyepoxy resins useful in conjunction with the present invention which willimpart to the final composition the desired physical, chemical andelectrical character are those which are prepared from the reaction ofan epihalohydrin, specifically epichlorohydrin and2,2-bis(4-hydroxyphenyl)-propane (Bisphenol-A). It is further required,in order to obtain the desirable elastomeric characteristics of thisinvention, that the epoxy resins contain a very restricted number of OHgroups, such OH groups enhancing undesirable crosslinking. It has beenfound that the epoxy resins which are useful in connection with thepresent invention shall be liquid and have an epoxide equivalent of from200 and preferably from about 170-185 with an average hydroxyl contentof 0 to 0.2 OH group per molecule. Shown in the table below are typicalepoxy resins which are useful in connection with this invention.

The anhydrides, which have been found to be useful in connection withthe present invention are those having the general formula where R isselected from the group consitsing of H and hydrocarbon groups and n isan integer up to about 3 and m is l or 2. Typically preferred anhydridesare succinic anhydride, methyl succinic anhydride and glutaricanhydride. It has been found that when n is eight or more, the finalcured epoxy resin prepared with the anhydrideglycol reaction producttends to be cheesy and have but little or no elastomeric qualities. Theliquid character of the anhydride-glycol reaction product makespossible, in conjunction with the other liquid components, a readilymixed system which is solventless in nature. The corresponding acids ofthe present anhydrides have been found to be not useful since such acidswhen used to prepare the curing agent for epoxy resins according to thepresent invention split off" water, enhancing a polyester reaction whichproduces non-elastorneric final materials.

The glycols which are useful in connection with the present inventionare those which contain at least four carbon atoms and up to about 12carbon atoms, such glycols also being further characterized by the factthat they have only terminal hydroxyl groups. Mixtures of such diols canbe used. It will be apparent that bya droxyl groups intermediate to theend groups would again detract from the elastomeric quality of thepresent materials.

The tertiary amines which are useful as accelerators 4 nel through whichthe anhy ride is added to the flask and heated to a temperature of about115 C. In a typical reaction the source of heat is then removed and theglycol slowly added from a dropping funnel with stirring.

include all such amines. These amines accelerate the 5 Since thereaction in exothermic, the addition of glycol cure and direct it toproduce long chain elastomeric is regulated to hold the temperature inthe flask at from products in which the carboxyl groups react primarilyabout 110 to 120 C. After addition of the glycol is with the epoxidegroups rather than any hydroxyl groups complete, the contents of theflask are allowed to cool to which latter reaction produces undesirablecross-linking. 80 C. and removed. It is particularly important that theTypical of useful tertiary amines are dimethylbenzyl- 1O temperature ofreaction of the anhydride and the glycol amine,trisdimethylaminomethylphenol, sold as DMP-3O in acid be below about 120C. For example, when reby Rohm and Haas Company;dimethylaminomethylactants comprising one mole of methyl succinicanhyphenol, sold as DMP-lO by Rohm and Haas Company; dride, one mole ofsuccinic anhydride and one mole of and Z-ethylhexanoate oftrisdimethylaminomethylphenol, 1,5-pentanediol were heated for fourhours at 100 C., sold as Shell Catalyst D by the Shell Chemical Comthedesired present curing agent addition product of anpany. Other tertiaryamines will, of course, occur to hydride and glycol was obtained.However, when this those skilled in the art. In lieu of using thetertiary amine PIOEhlCt Was f r h a d f r two h urS at 150 C., it assuch in connection with the present invention, it may s nd that thereaction had PFOCBeded t0 the Point be utilized also as an integral partof the anhydride-glycol where there was Present about 75 PercentPolyester and reaction product. Thus, there may be reacted togetherPflcfiht llflfeacted flhhydfide- Ltkfiwise, it Was found one mole ofmethyldiethanolamine, one mole of succinic that Whfln the Originalanhydride and glycol ingredients anhydride and one mole of glutaricanhydride to provide as above were heated for two hours at 150 C., theabove a i l h i the f l undesired ratios of polyester and unreactedanhydride 0 0 were obtained. It will thus be seen that it is necessary25 to restrict the temperature of reaction to about 120 C. CHPCH2 O CCHQ CH2 G OH or below. The following examples illustrate the prepara-CHFN tion of the anhydride-glycol curing agent of the present 7 Iinvention. In each case the ingredients set forth were CHPCH' 0 ifCut-CH" 1 OH heated for one-half hour at 115-120 C. to obtain a com- 0 Oposition having the designated actual equivalent weight in which thecuring agent and tertiary amine are comwhich, it will be seen, is veryclose to the listed theoretical bined in one compound. Also, there maybe reacted equivalent weight.

TABLE II Theo- Actual Ex. Anlrydnde Glycol rotical E.W.

1 1 Methylsuccinic, 1 Succinic. 1-1,5-pentanedi0l 159 157 2 3Glutaric1-tricthanolamine 163.6 160 3 2 Giutaric l-neopontyl 166 168 4 1Suecinic, 1 Glutario 1-X-2635 (Dow) 275 234 CH: (HO-CCO('3-O-CCOH) 5. 1Glutaric, 1 Succinic l-LS-pontanediol 159 1-31 6..." 2 Succinic c c i do152 151 a do 166 168 1-1,9-nonanodi0l 194 196 l 1-1.6-hoxanedioL. 173174 l I ...do l-clicthylenc glyc 167 16S 1L- 1 Succinio, 1Metl1ylsuccinic l-lA-butanediol 152 151 together one mole oftriethanolamine and three moles of glutaric anhydride to provide amaterial having the forrnlua:

i i N(CH2-CH2OC-CH2CH2CHz-C-OH)3 which, again, is useful in connectionwith the present invention as a composite curing agent-tertiary amineaccelerator and director material. Generally, in order to obtain theproper amount of acid equivalents and the proper amount of tertiaryamine, the three-component material is used in conjunction with aglycol-anhydride reaction product as described.

It is important in preparing the anhydride-glycol curing agent of thepresent invention that the anhydride and glycol be reacted in the ratioof two moles of anhydride to one mole of glycol. Lesser amounts ofanhydride promote an undesirable polyester reaction while largerproportions result in the presence of unreacted anhydride which promotesundesirable cross-linking of the epoxy resin. In preparing the curingagent, typically there is used a three-necked round bottom flaskequipped with heating mandrel, stirrer, thermometer and dropping fun-Example 12 This example illustrates the criticality of the reactiontemperature which must be adhered to in preparing the anhydride-glycolcuring agents of the present invention. There were added together asdescribed two moles of methyl succinic anhydride and one mole of1,5-pentanediol. One portion of the mixture was heated for eight hoursat 100 C. to give a completely reacted adduct which was useful inconnection with the present invention. On the other hand, when anotherportion of such a mixture was heated for two hours at 150 C., it wasfound that there was present about 20 percent of unreacted anhydride andabout percent poiyester, making this composition unusable in connectionwith the invention.

In curing the epoxy resins of the present invention, it has been foundthat in order to obtain the elastomeric qualities required, the reactionbe accomplished without a polyester reaction. In this connection, it hasbeen found that the curing agent shall 'be used in such amounts thatthere are present from about 0.85 to 1.0 acid equivalent of curing agentfor each epoxide equivalent and that the reaction be carried out attemperatures ranging from 175 C. for from eight hours to one hour, the

reaction being of a time-temperature nature. Preferably, the reaction iscarried out for about four to eight hours at 125l50 C. and mostpreferably for eight hours or more. It has been found that the additionof from about 0.5 to 2 percent by weight of tertiary amine based on theweight of epoxy resin satisfactorily accelerates and directs thereaction to give the desired cure in a convenient time. The followingexamples illustrate the curingof epoxy resins according to the presentinvention, 1t being evident that such examples are typical only of theinvention and are not to be taken as limiting in any way. All parts areby weight.

Example 13 There were added to 52 parts of Dow 332 LC epoxy resin, 48parts of the curing agent of Example 5 consisting of the reactionproduct as described of one mole each of glutaric anhydride, succinicanhydride and 1,5- pentanediol along with three parts of a finelydivided sil ca filler and 0.52 part of Shell Catalyst D. This materialwas used as an adhesive for low carbon steel panels, the material beingapplied at a thickness of 5 mils and cured for 16 hours at 150 C., therebeing one square inch of adhered steel panel area. This test piece aftercure was tested on an Instron Tester at .05 inch per minute head speedto give a tensile strength of 1730 p.s.1. The examples shown in thefollowing table were all carried out using Dow DER 332 LC epoxy resinhavlng an epoxide equivalent of 173, there being used one part perpentyl glycol to provide a reaction product having an equivalent weightof 251 as compared to a theoretical equivalent weight of 261. When thismaterial was mixed with Dow 332 LC epoxy resin in such proportions thatthere was present 0.85 acid equivalent for each epoxide equivalent,along with 1 percent of Shell Catalyst D based on the weight of theepoxy resin and cured for 16 hours at 150 C., there was produced a finalcomposition which was rubbery at room temperature but crumbly at 100 C.

Example 24 This example illustrates the use of compositeanhydrideglycol-tertiary amine reaction products as combination curingagent-accelerator and director materials in curing the epoxy resins ofthe invention. There was combined with Dow 332 LC epoxy resin in suchamount as to provide one epoxide equivalent a curing agent prepared asabove from two moles of methyl succinic anhydride and one mole of1,5-pentane diol in such amount that there was present 0.9 equivalent ofcarboxyl groups per equivalent of epoxy resin along with the reactionproduct of one mole of triethanolamine and three moles of glutaricanhydride as described above, the quantity of such materal being suchthat there was present an additional 0.1 equivalent of carboxyl perepoxide groups to give a total of 1.0 equivalent of carboxyl for eachepoxide equivalent. The amount of amine present in this compositionmaterial Was equivalent to 2 percent by weight of dimethylbenzylhundredparts of epoxy resin of Shell Catalyst D. amlne based on the weight ofthe epoxy resin. When TABLE III 16 hrs. at 150 C. 3 Days at 135 C. 7Days at 160 0. Cute Aging Aging COOH/ Ex. Curing Agent Epoxide Eq. RatioT.S Elonga- T.S., Elonga- T.S., Elongap.s.1. tion, p.s.i. tion, p.s.i.tion,

Percent Percent Percent g b inie, i-diethyiene glycol 85 075 143 1, 075176 1. 00 500 358 535 306 2, 310 320 2. e1;hy15uccinic,1-1,5-pentanediol 0.85 1,690 220 1,008 260 4, 350 330 1. 00 750 480 595344 1, 070 183 16 l-methylsuccinic, 1succi.nic, 1-1,5- 0. 85 2, 450 224770 303 350 200 pentanediol. 1. 00 842 368 1, 370 322 3, 460 33s g ilm,1-1,5-pentanediol 85 500 318 570 313 230 145 1. 00 2, 900 143 1, 930 1653, 000 176 18 2-succinic, Ldiethylene glycol 0. 85 1, 557 94 1, 630 72From the above examples it will be quite evident that there is producedby the present invention epoxy resin compositions which arecharacterized by good tensile strength and elastomeric qualities.

There were added to Epon 828 and Dow 332 LC a curing agent like that ofExample 1 in the amounts shown in Table IV below along with 1 percent ofShell Catalyst D based on the weight of the epoxy resin. This materialwas cured for 16 hours at 150 C. with the following results.

TABLE IV COOH/ Tensile Percent Ex. Resin Epoxide Strength ElongationExample 23 This example illustrates the undesirability of epoxy resinswhen cured with the present curing agents wherein n in the anhydrideused to prepare the curing agent is a number in excess of three. Therewas prepared according to Example 1 a curing agent consisting of twomoles of n-octenyl succinic anhydride and one mole of neocured as above,this material provided an epoxy resin characterized by salutaryelastomeric qualities both at room temperature and at elevatedtemperatures.

From the above, it will be quite evident that the very specificparameters set forth must be adhered to in order to provide a usefulmaterial in accordance with the invention.

There are provided then by the present invention epoxy resincompositions which are possessed of efficacious physical, chemical andelectrical properties, including an elastomeric or rubbery quality atroom temperature and elevated temperatures which makes them particularlyuseful as adhesives and as dipping or coating materials which may beused to elfectively bond and seal components which are subjected tomechanical stresses at various temperatures.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. A composition of matter comprising the heat reaction product of (1) acomplex epoxide resin containing an average of more than one epoxidegroup per molecule and comprising the reaction product of2,2-bis-(4-hydroxyphenyl)-propane and epihalohydrin, said epoxide resinhaving an epoxide equivalent of about to 200 and up to 0.2 hydroxylgroup per molecule, (2) a curing agent for said epoxy resin comprisingthe heat reaction product I at temperatures of up to about 120 C. of (a)two moles of anhydride having the formula where R is selected from H andmethyl groups, and m is an integer up to 2, and (b) one mole of diolcontaining only terminal hydroxyl groups and having up to about 12carbon atoms and (3) tertiary amine, said curing agent being present inan amount to provide from about 0.85 to 1 acid equivalent per equivalentof epoxide, said amine being present in the amount of from about 0.25 to2 percent by weight based on the weight of said epoxide resin.

2. A composition of matter comprising the heat reaction product of (1) acomplex epoxide resin containing an average of more than one epoxidegroup per molecule and comprising the reaction product of2,2-bis-(4-hydroxyphenyl)-propane and epihalohydrin, said epoxide resinhaving an epoxide equivalent of about 170 to 185 and up to 0.2 hydroxylgroup per molecule, (2) a curing agent for said epoxy resin comprisingthe heat reaction product at temperatures of up to about 120 C. of (a)two moles of anhydride having the formula R-GC Where R is selected fromH and methyl groups, and m is an integer up to 2, and (b) one mole ofdiol containing only terminal hydroxyl groups and having up to about 12carbon atoms and (3) tertiary amine, said curing agent being present inan amount to provide from about 0.85 to 1 acid equivalent per equivalentof epoxide, said amine being present in the amount of from about 0.25 to2 percent by weight based on the Weight of said epoxide resin.

3. A composition of matter comprising the heat reaction product of (l) acomplex epoxide resin containing an average of more than one epoxidegroup per molecule and comprising the reaction product of2,2-bis-(4-hydroxyphenyl)-propane and epihalohydrin, said epoxide resinhaving an epoxide equivalent of about 170 to 200 and up to 0.2 hydroxylgroup per molecule, (2) a curing agent for said epoxy resin comprisingthe heat reaction product at temperatures of up to about 120 C. of (a)two moles of anhydride having the formula where R is selected from H andmethyl groups, and m is an integer up to 2, and (b) one mole of diolcontaining only terminal hydroxyl groups having up to about 12 carbonatoms and containing at least one tertiary amino group.

4. A composition of matter comprising the heat reaction product of (l) acomplex epoxide resin containing an average of more than one epoxidegroup per molecule and comprising the reaction product of2,2-bis-(4-hydroxyphenyl)-propane and epihalohydrin, said epoxide resinhaving an epoxide equivalent of about 170 to 200 and up to 0.2 hydroxylgroup per molecule, (2) a curing agent for said epoxy resin comprisingthe heat reaction product at temperatures of up to about C. of (a) twomoles of anhydride selected from the group consisting of succinicanhydride, methylsuccinic anhydride and glutaric anhydride and mixturesthereof, and (b) one mole of diol containing only terminal hydroxylgroups and selected from the class consisting of 1,5-pentanediol,1,9-nonar1ediol, neopentyl glycol, diethylene glycol, 1,4-butanediol and1,6-hexanediol and mixtures thereof and (3) tertiary amine, said curingagent being present in an amount to provide from about 0.85 to 1 acidequivalent per equivalent of epoxide, said amine being present in theamount of from about 0.25 to 2 percent by weight based on the weight ofsaid epoxide resin.

5. A composition of matter comprising the heat reaction product of (l) acomplex epoxide resin containing an average of more than one epoxidegroup per molecule and comprising the reaction product of2,2-bis-(4-hydroxyphenyl)-propane and epihalohydrin, said epoxide resinhaving an epoxide equivalent of about to 200 and up to 0.2 hydroxylgroup per molecule, (2) a curing agent for said epoxy resin comprisingthe heat reaction product at temperatures of up to about 120 C. of (a)one mole of glutaric anhydride and one mole of succinic anhydride, and(b) one mole of 1,5-pentanediol and (3) tertiary amine, said curingagent being present in an amount to provide from about 0.85 to 1 acidequivalent per equivalent of epoxide, said amine being present in theamount of from about 0.25 to 2 percent by weight based on the weight ofsaid epoxide resin.

6. A composition of matter comprising the heat reaction product of (1) acomplex epoxide resin containing an average of more than one epoxidegroup per molecule and comprising the reaction product of2,2-bis-(4-hydroxyphenyl)-propane and epihalohydrin, said epoxide resinhaving an epoxide equivalent of about 170 to 200 and up to 0.2 hydroxylgroup per molecule, (2) a curing agent for said epoxy resin comprisingthe heat reaction product at temperatures of up to about 120 C. of (a)one mole of methyl succinic anhydride and one mole of succinicanhydride, and (b) one mole of 1,5-pentanediol and (3) tertiary amine,said curing agent being present in an amount to provide from about 0.85to 1 acid equivalent per equivalent of epoxide, said amine being presentin the amount of from about 0.25 to 2 percent by weight based on theweight of said epoxide resin.

7. A compositon of matter comprising the heat reaction product of (1) acomplex epoxide resin containing an average of more than one epoxidegroup per molecule and comprising the reaction product of2,2-bis-(4-hydroxyphenyl)-propane and epihalohydrin, said epoxide resinhaving an epoxide equivalent of about 170 to 200 and up to 0.2 hydroxylgroup per molecule, (2) a curing agent for said epoxy resin comprisingthe heat reaction product at temperatures of up to about 120 C. of (a)two moles of glutaric anhydride, and (b) one mole of neopentyl glycoland (3) tertiary amine, said curing agent being present in an amount toprovide from about 0.85 to 1 acid equivalent per equivalent of epoxide,said amine being present in the amount of from about 0.25 to 2 percentby weight based on the weight of said epoxide resin.

References Cited by the Examiner UNITED STATES PATENTS 2,868,767 1/1959Cyba et a1. 260-47 2,900,364 8/1959 Wasserman 26047 FOREIGN PATENTS586,026 10/1959 Canada.

WILLIAM H. SHORT, Primary Examiner.

C. A. WENDEL, Assistant Examiner.

1. A COMPOSITION OF MATTER COMPRISING THE HEAT REACTION PRODUCT OF (1) ACOMPLEX EPOXIDE RESIN CONTAINING AN AVERAGE OF MORE THAN ONE EPOXIDEGROUP PER MOLECULE AND COMPRISING THE REACTION PRODUCT OF2,2-BIS-(4-HYDROXYPHENYL)-PROPANE AND EPIHALOHYDRIN, SAID EPOXIDE RESINHAVING AN EPOXIDE EQUIVALENT OF ABOUT 170 TO 200 AND UP TO 0.2 HYDROXYLGROUP PER MOLECULE, (2) A CURING AGENT FOR SAID EPOXY RESIN COMPRISINGTHE HEAT REACTION PRODUCT AT TEMPERATURES OF UP TO ABOUT 120*C. OF (A)TWO MOLES OF ANHYDRIDE HAVING THE FORMULA
 3. A COMPOSITION OF MATTERCOMPRISING THE HEAT REACTION PRODUCT OF (1) A COMPLEX EPOXIDE RESINCONTAINING AN AVERAGE OF MORE THAN ONE EPOXIDE GROUP PER MOLECULE ANDCOMPRISING THE REACTION PRODUCT OF 2,2-BIS-(4-HYDROXYPHENYL)-PROPANE ANDEPIHALOHYDRIN, SAID EPOXIDE RESIN HAVING AN EPOXIDE EQUIVALENT OF ABOUT170 TO 200 AND UP TO 0.2 HYDROXYL GROUP PER MOLECULE, (2) A CURING AGENTFOR SAID EPOXY RESIN COMPRISING THE HEAT REACTION PRODUCT ATTEMPERATURES OF UP TO ABOUT 120*C. OF (A) TWO MOLES OF ANHYDRIDE HAVINGTHE FORMULA